The present invention relates to an improved process for preparation of overbased materials, providing materials which are low in chlorine content.
Overbased materials have been long known and are important lubricating oil additives. These materials are metal salts of acidic organic compounds. Overbased materials are single phase, homogeneous, and generally Newtonian systems characterized by a metal content in excess of that which would be present according to the stoichiometry of the metal and the particular acidic organic compound reacted with the metal. Such materials are often prepared by mixing together an oil-soluble acid material, greater than 1 equivalent of base, such as a calcium base, and a promoter. Often the promoter includes an inorganic halide such as calcium chloride. This material is referred to as a co-promoter, and is believed to function by increasing the solubility of a calcium base (such as calcium hydroxide) in the reaction medium. In some cases the overbased material is further reacted with an acidic gas such as carbon dioxide. The following patents generally illustrate this and other related processes:
U.S. Pat. No. 3,256,186, Greenwald, Jun. 14, 1966, discloses a process for producing carbonated basic metal compositions. The process comprises carbonating a mixture of (A) one equivalent of an acidic substance, (B) at least about 0.1 equivalent of an alcohol per equivalent of (A), (C) from about 0.1% to about 5% by weight of (A) of an inorganic halide selected from the class consisting of ammonium halides, alkali metal halides, and alkaline earth metal halides, and (D) at least about 2 equivalents of an alkaline earth metal base per equivalent of (A). Especially useful as (B) are mixtures of methanol with a higher monohydric alcohol. Chlorides of ammonium, sodium, barium, and calcium are especially effective as (D).
U.S. Pat. No. 3,372,116, Meinhardt, Mar. 5, 1968, discloses preparation of basic metal phenates and salicylates. It discloses treatment of a polyisobutene-substituted phenol in mineral oil with calcium oxide, propanol, and acetic acid, followed by contacting with carbon dioxide. It also discloses treatment of a material with a mixture of methanol, amyl alcohol, and isobutyl alcohol containing calcium hydroxide and calcium acetate, followed by treatment with carbon dioxide. It lists suitable promoters as including carboxylic acids containing about 1-100 carbon atoms and metal salts thereof. Suitable monocarboxylic acids include formic, acetic, propionic, butyric acids, and so on.
U.S. Pat. No. 4,597,880, Eliades, Jul. 1, 1986, discloses a one-step process for preparation of overbased calcium sulfonate greases. The essential ingredients in the process include a liquid carrier, a sulfonic acid, calcium oxide or hydroxide, water-soluble carboxylic acids including acetic acid, preferably an alcohol or alkoxyalcohol of 1 to 8 carbon atoms, such as methanol or methyl (or ethyl) cellosolve, and water; the mixture is carbonated.
U.S. Pat. No. 3,155,617, Voorhees, Nov. 3, 1964, discloses a means of activating calcium oxide (prepared from roasting calcium carbonate), so that it is useful in the methanol process for preparing dispersions of calcium carbonate. The calcium oxide is treated in methanol suspension with a small amount of an acid such as HCl, sulfamic acid, H.sub.2 SO.sub.4, HNO.sub.2, HNO.sub.3, or various organic acids such as acetic acid.
It is not always desirable, however, to have chloride present in an overbased material, because of its potentially corrosive properties and because of environmental concerns about residual chlorine in waste oils. Accordingly, the present invention provides an efficient process for preparing overbased materials which does not require the use of chloride-containing promoters or co-promoters.